The present invention relates to apparatus for dispensing a liquid and, more particularly, to a dispensing apparatus for simultaneously dispensing predetermined equal volumes of liquid to a plurality of receivers.
Particularly in the field of microbiology, there is need to determine the results of adding different ingredients, such as drugs, or varying quantities of the same ingredient, to equal volumes of the same liquid, such as a microbiological broth in which bacteria have been grown. A common method of carrying out such a test is to use a tray having an array of wells each having an equal volume of liquid and adding the various ingredients. It will be appreciated that manually placing the liquid in each well is time consuming, expensive, and tends to introduce inaccuracies.
Prior art apparatus for simultaneously dispensing like volumes of liquid to an array of wells is shown in FIGS. 1 and 2. The apparatus includes a standard 20, supported by a base 22, releasably carrying a horizontally extending dispenser module 24 having an apertured top surface with dependent walls 26 each forming a dispenser chamber 28 in alignment with a corresponding well. Clamped in sealed relationship across the module top surface is a diaphragm 29; a horizontal plate 30 having a downwardly extending arrangement of plungers 31 overlies the module, each plunger being in registration with a corresponding dispenser chamber and each being exactly the same size. Plate 30 is manually movable toward and away from the dispenser module by means a rack and pinion drive. Operation of the drive causes the plungers to deflect downwardly diaphragm portions, to reduce the volume of each dispenser chamber by an equal amount as shown in FIG. 2. After the lower or nozzle ends of walls 26 are inserted in a pan of liquid beneath the liquid level, retraction of the plunger plate permits the diaphragm, due to its resiliency, to return to its FIG. 1 position, thus drawing an equal volume of the liquid into each dispenser chamber. Replacement of the pan with the tray and operation of the drive effects release of the liquid from the dispenser chambers into the wells.
The diaphragm is integrally clamped to the dispenser module, and both are replaced after each use because the module is contaminated by the liquid. Another reason the diaphragm is replaced after each use is that, as diaphragm portions enter the chambers, the diaphragm may be contaminated by the liquid. This prior art system requires an expensive drive and alignment slide to maintain the precise horizontal posture of the plate as it moves from its retracted position. Movement of the plate out of a horizontal plane results in unequal volumes of liquid being drawn into the various dispenser chambers. Additionally, as the drive is manually operable, operator judgment is required in determining when the plunger plate has reached its fully extended position. For example, if the operator makes a mistake due to inattentiveness or attempting to operate the apparatus too quickly, while equal volumes will be introduced into each dispenser chamber, such volumes will be less than the predetermined desired volumes, possibly rendering the test results invalid.